Beat butter and sugar at medium speed until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in melted chocolate. Turn mixer to low speed; add flour mixture alternately with buttermilk mixture and beat until well blended. Turn to medium speed and beat until smooth and creamy. Pour into pans, spread evenly and bake 25 to 30 minutes or until a tester inserted in center comes out clean. Let cool in pans on wire racks 10 minutes. Remove from pans and finish cooling on racks.

To prepare frosting, whisk espresso powder and vanilla with 2 tablespoons milk in a small bowl.

Beat butter at medium speed until creamy. Turn to low speed and gradually beat in powdered sugar. Add melted chocolate and milk mixture; increase mixer speed and beat until smooth and creamy. If necessary, add more milk to make spreadable.

Place one cake layer on plate. Spread with about 2/3 cup frosting. Cover with second cake layer and frost sides and top of cake with remaining frosting. Sprinkle chopped chocolate in a circle around top edge of cake, if desired.